1. Technical Field
The present invention concerns pattern recognition and object recognition technologies, and more specifically, the invention relates to a head-top detecting method, a head-top detecting system and a head-top detecting program for accurately detecting the head-top of a human face from an image of the human face.
2. Related Art
With recent advancements of pattern recognition technologies and information processors such as computers, the recognition accuracy of text and sound has been dramatically improved. However, in the pattern recognition of an image of a human, an object, the landscape and so on, e.g., an image scanned from a digital still camera or the like, it is still difficult to accurately and quickly identify whether a human face is visible in the image or not.
However, automatically and accurately identifying whether a human face is visible in the image or not (with a computer) and who the human is has been extremely important to establish a living body recognition process, improve security, accelerate criminal investigations, speed up image data reduction and retrieval and so on. In this regard, many proposals have been made.
In JP-A-9-50528, the existence of a flesh color area is first determined in an input image, and the mosaic size is automatically determined in the flesh color area to convert a candidate area into a mosaic pattern. Then the existence of a human face is determined by calculating the proximity from a human face dictionary and mis-extraction due to the influence of a background and the like can be reduced by segmenting the human face. Thereby the human face can be automatically and effectively detected from the image.
In JP-A-8-77334, extraction of the feature point of a face image to be used for distinguishing each individual and group (for example, an ethnic group) is automatically and easily performed at a high speed by using a predetermined algorithm.
Incidentally, with regard to a required photo of a human face (which is a face image) for a passport, a photo ID card and the like, many photographic pose requirements are set in detail such as the size of the photo, the direction to which the human face faces, and the size and location of the human face within the photograph.
For example, not to mention the requirements for no background and no accessory such as a hat, there are detailed regulations requiring that the human face point to the front, that the human face be located in the center of photo, that the head-top of the face be located within a specific distance relative to the lower frame of the photo, and so on. In principle, a photo of a face image that is outside of the regulations is not adopted.
However, it is impractical to retake a photo simply because the size and location of the face in the photo is slightly out of regulation, although it may be rational if the human face is not facing the front or if an accessory such as a hat is worn. This causes a problem of imposing considerable labor and cost on a user.
For this reason, a method of solving the above problems has been examined by using digital image processing which has developed significantly in recent years.
For example, the following method has been examined to solve the problems. First, digital image data of a human face is directly obtained by a digital still camera or the like using an electronic image pickup device such as a CCD or a CMOS. On the other hand, the digital image data may be obtained from an analog photo (silver salt photo) of the human face by using an electronic optical image scanner. Once the digital image data is obtained, easy image processing such as zooming in/out and moving the face image are performed by using an image processing system comprising a general-purpose computer such as a PC and general-purpose software without damaging the innate characteristics of the human face.
Although it is possible to manually perform the above process by using general-purpose I/O devices such as a mouse, a keyboard and a monitor when the number of images to be processed is small, it becomes necessary to perform the process automatically by using the aforementioned conventional techniques when the number of images increases.
To realize the automation of image processing for a human face, however, it is necessary to accurately recognize a face outline, especially a head-top location of a human face, which does not necessarily generate a clear line due to a person's hairstyle, the lighting and other conditions present while taking the picture, and which cannot be accurately scanned in many cases by a conventional edge detection filter. Therefore, it is difficult to automatically recognize the head-top.
The present invention has been achieved to solve the aforementioned problems. Therefore, one object of the invention is to provide a novel head-top detecting method, a head-top detecting system and a head-top detecting program capable of detecting a head-top of a human face by accurately and quickly detecting a head-top of a human face, which is difficult to automatically detect by an edge detection technique.